Relatively speaking in relation to our society it was not, however in relation to other non-Greek ancient societies at the time it was, but not as free as Ancient Athens. All Spartan males were required to serve in the military. Men and women were educated in the subjects of war, battle, poetry and dance. Male children were separated from their parents at seven years old, and began their agoge (a program where the child was indoctrinated in devotion to the State and military training). This was required of all male children. Sparta, as a society, did not produce the level of literature, art, architecture that their biggest city-state competitor Athens had produced. However, it's important to keep in mind that since the Spartans seldom wrote anything down, most of what we know about Sparta comes from the descriptions given by their bitter rivals the Athenians.
The helots, descendants of an earlier conquered race of inhabitants from the region of Laconia, near where Sparta was located, were enslaved by the Spartans and forced to labor on large estates. When Spartan warriors were in shortage, Helots were forced into the military. They were slaves-for-life, however they could gain Spartan citizenship if they fought bravely in battle, as they sometimes did to augment Spartan troops. It's important to note however that slavery was a part of life in all ancient societies, including ancient Athenian society. So the Spartans were not unique in this regard, and slavery has been, and continues to be, practiced throughout most of human history.
Also what's interesting to note is that the founders of the United States borrowed their idea of a three-branched government with checks and balances from the Spartans. Sparta had two kings, who served as commanders-in-chief of the Spartan military, and each King could veto the other in military affairs. Then there was the Gerousia, a body of 28 elders elected by democratic vote amongst the Spartan citizenry. The Gerousia was a kind of Senate, that could write bills, but the passage of such a bill into law required the approval of the Spartan citizenry through democratic vote. There was also the Ephors, five elders who were chosen by popular election who had most of the political control in Sparta. For example, the Ephors could strike down a law passed by the Gerousia as unconstitutional, similar to the power of the United States Supreme Court. The Ephors also had the power to remove a King if that King broke Spartan law. This political sophistication of checks and balances was one that not even Ancient Athens possessed.
Sparta was certainly more "free" than any state under Persian domination. Classicist and military historian Victor Davis Hanson, who previewed the film and wrote a foreword for a movie tie-in book, says in his article "300: Fact or Fiction",
True, 2,500 years ago, almost every society in the ancient Mediterranean world had slaves. And all relegated women to a relatively inferior position. Sparta turned the entire region of Messenia into a dependent serf state.
However, he goes on to say that...
in the Greek polis alone, there were elected governments, ranging from the constitutional oligarchy at Sparta to much broader-based voting in states like Athens and Thespiae [...] Most importantly, only in Greece was there a constant tradition of unfettered expression and self-criticism, unlike the Persian Empire, where speaking against official policy of the emperor—a living god—was blasphemy.
all openly questioned the subordinate position of women, whilst Alcidamas
lamented the notion of slavery. With this in mind, Hanson argues that...
such openness was found nowhere else in the ancient Mediterranean world. That freedom of expression explains why we rightly consider the ancient Greeks as the founders of our present Western civilization.
For more information on the intricacies of Spartan society, see Paul Cartledge
's book The Spartans: The World of the Warrior Heroes of Ancient Greece